This invention relates to an optical switching device and, more particularly, to an electrically controlled switching device for individually directing a plurality of arbitrarily polarized optical beams to selected output ports.
Signal processing systems often employ multiple parallel processors which permit many operations to take place concurrently. These so called parallel processing architectures typically require switching devices capable of efficiently transferring the data signals between such parallel processors. It is particularly advantageous to use optical switching devices to selectively interconnect the multiple parallel processors. For example, optical signal beams provide greater operating bandwidths and superior immunity to electromagnetic interference as compared with electrical signals.
These optical switching devices must be capable of spatially switching large numbers of light beams while preserving the integrity of the signals communicated by such light beams. One approach generally used in the fabrication of these switching devices is to utilize a plurality of elementary switching cells which in combination provide the overall switching capacity of the device. In these switching devices, it is highly desirable to reduce the number of elementary switching cells required to switch a given number of light beams so that, for instance, the switching device becomes more compact while having lower fabrication costs.
An optical device for switching light beams is proposed by J. B. McManus, R. S. Putnam, and H. J. Caulfield in the paper entitled "Switched holograms for reconfigurable optical interconnection: demonstration of a prototype device", Vol 27, Applied Optics, pp. 4244-4250, Oct. 15, 1988. The device proposed by McManus et al.,(hereinafter McManus), utilizes a plurality of polarization-dependent switching cells arranged in a two-dimensional matrix which, in general, can have M columns and N rows of switching cells. Each switching cell comprises a polarizing beamsplitter and a spatial light modulator (SLM) which cooperate to selectively direct light beams externally applied to the matrix to selected outputs. Several disadvantages of the device proposed by McManus are that use of polarization-dependent switching cells can reduce light beam intensity (as may occur if a polarizer is used to polarize light to be used in a polarization-dependent system) and connections between such polarization dependent switching devices may require the use of polarization-maintaining fibers. Moreover, the device proposed by McManus is confined to a two-dimensional arrangement of switching cells (e.g., a single two-dimensional switching matrix), as McManus does not suggest how his device can be expanded into a three-dimensional arrangement of switching cells (e.g., a succession of identical two-dimensional matrices positioned parallel to each other). A device having such three-dimensional expansion capability can significantly increase the universe of selectable output ports to which the light beams can be switched. For example, if Q is the number of successive two-dimensional matrices positioned parallel to each other, then the number of selectable output ports will increase by a Q factor.
Polarization-independent types of switching devices have been suggested that enable an arbitrarily polarized light beam (i.e. an unpolarized light beam) to be selectively directed along a predetermined path. One example of such a polarization-independent switch is described by Wagner and Cheng in "Electrically Controlled Optical Switch For Multimode Fiber Applications," Applied Optics, Vol. 19, No. 17, September 1980, pp 2921-2925. However, Wagner et al. do not suggest any two-dimensional arrangement for their switches, and much less a three-dimensional switching arrangement.
Accordingly, one object of the invention is to provide a two-dimensional optical switching device which can be controlled to individually and simultaneously direct arbitrarily polarized light beams received by each of multiple polarization-independent switching cells thereof.
Another object of the present invention is to provide a polarization-independent optical switching device which can be three-dimensionally expanded to provide additional selectable output ports for the light beams switched by the device.